Mercury cementation from chloride solutions using iron, zinc and aluminium

The reaction order was 1.08+/-0.05 with respect to mercury concentration. The reaction efficiency is strongly dependent on pH. For each metal in study, an ideal pH was established: 4.0 to 5.0 for zinc, 3.0 for iron and 3.0 to 4.0 for aluminium. Tests carried out with zinc particles having different grain sizes and different dosages show that the specific surface of the sacrificial metal and the mass of metal are important parameters in the removal obtained. The presence of Zn2+ as ZnSO4 in the initial solution, in concentrations of 0.7 to 6.8 g Zn/l, showed that the presence of such a cation did not affect the initial rate of mercury cementation, although for long residence rimes it favoured the cement redissolution. This phenomenon occurred when the ratio between the moles of ionic mercury and moles of dissolved zinc was equal to or less than 3x10(-5) This work can be applied to the recovery of mercury in leachates, produced in an integrated sludge treatment process. The optimum conditions found for synthetic mercuric solutions were tested with a real mercury leachate. The results shown that is possible to obtain 0.08 ppm of Hg in the final solution.